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Author Topic: G5RV Jr/ Is it really that hard to tune?  (Read 2350 times)
KF4CZV
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Posts: 142




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« on: July 07, 2010, 04:21:38 PM »

Just picked up a G5RV Jr. and haven't put it up yet. Everything I read about these (including the maker's instruction sheet) say that the rig's tuner won't work and an external manual tuner is a must. Nothing else will do! You'll blow the roof off your house if you try to tune it with your rig! Are they really that hard to tune? My rig is an older Yaesu FT900 with the ATU2 internal tuner. I'll only be running 100 watts. I've read that my rig's tuner was one of the better ones and can usually handle what the newer ones won't. The only other tuner I have is an LDG Z100. Does anyone have experience with this rig/antenna combo? The antenna will be nowhere near an ideal install. Thanks!

Terry
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WX7G
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Posts: 5920




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« Reply #1 on: July 07, 2010, 05:11:25 PM »

The only way to know is to fire it up.
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VE3WMB
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Posts: 282




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« Reply #2 on: July 07, 2010, 05:19:31 PM »

Terry it will depend a lot on the matching range of the internal tuner in your rig. Generally the internal auto-tuners don't have the sort of range that you would find on the LDG Z100.  

For what it is worth, I am using a double-sized G5RV (ie 204 ft long) at my cottage. I have a balun attached to the 66ft of window-line and about 15 feet of LMR-400 coax going to my LDG Z100 Pro.
I easily get an acceptable match on all bands from 160m through 6m with this combination, with the
exception of 80m where the matching is iffy in some places on the band.

I suspect that you will be ok with the G5RV junior and the Z100. The internal tuner may not be able to
do as good a job at matching, it is hard to say until you try it.  Just be sure to keep the ladderline or twinlead feed off of the ground and
spaced away from anything metal (6 inches is probably a good distance). I also recommend using a short
run of very high quality coax as on some bands the SWR on the coax will be high, so you want to minimize
losses.

Best of luck and let us know how you make out.

Michael VE3WMB / VA2NB

Just picked up a G5RV Jr. and haven't put it up yet. Everything I read about these (including the maker's instruction sheet) say that the rig's tuner won't work and an external manual tuner is a must. Nothing else will do! You'll blow the roof off your house if you try to tune it with your rig! Are they really that hard to tune? My rig is an older Yaesu FT900 with the ATU2 internal tuner. I'll only be running 100 watts. I've read that my rig's tuner was one of the better ones and can usually handle what the newer ones won't. The only other tuner I have is an LDG Z100. Does anyone have experience with this rig/antenna combo? The antenna will be nowhere near an ideal install. Thanks!

Terry
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WB6BYU
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Posts: 13028




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« Reply #3 on: July 07, 2010, 06:10:55 PM »

It will depend to a large extent on the exact matching range of your tuner and the length of coax cable between
it and the antenna.  Just knowing the SWR doesn't help:  an SWR of 5 : 1 could be 10 ohms or 250 ohms (or
somewhere in between with inductive or capacitive reactance).   Some tuners will easily match 250 ohms but
not 10 ohms, and the difference between the two is a quarter wavelength of coax.

I would expect it to be a reasonable match on 10m, pretty tricky on 15m (unless you cable has enough loss
to reduce the SWR, in which case it won't be very efficient),  probably usable on 20m, and more dependent
on the line length on 40m.  80m will be hard to tune and pretty lossy.  The other bands might be usable if
you are lucky.

VK1OD has some good analysis of the G5RV on his web site:  just double the frequencies and they should
apply to your half-sized antenna:

http://vk1od.net/antenna/G5RV/index.htm
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KF4CZV
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Posts: 142




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« Reply #4 on: July 07, 2010, 06:49:03 PM »

Thanks for the replies! The coax jumper from my window feed through will only be 3-6 feet at most. Will that make any difference? I will check out that article.

Terry
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W6GX
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Posts: 2328




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« Reply #5 on: July 08, 2010, 10:05:35 AM »

I also have the G5RV Jr.  My friend also has one.  Between the two of us I can tell you the following based on our experiences...  Your experience may vary depending on antenna height, QTH, etc.

MFJ-998 tunes 75m to 6m except the lower half of 15m.
LDG-200Pro tunes 75m to 6m
LDG-1000Pro has difficulty tuning on most bands
Yaesu FT-950 internal tuner cannot tune this antenna.

I hope this helps.

Jonathan W6GX
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G3TXQ
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Posts: 1464




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« Reply #6 on: July 08, 2010, 11:33:03 AM »

Here are some typical mid-band impedances at the end of the coax section. I assumed the antenna was at 30ft over average ground, and the length of the coax jumper was 4ft:

80m: 0.3 - j190
40m: 10 - j26
30m: 18 - j120
20m: 11 - j30
17m: 31 - j150
15m: 2 - j60
12m: 1 - j35
10m: 24 - j14

80m, 15m and 12m look like a big "ask" for any tuner.

Steve G3TXQ
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W6GX
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Posts: 2328




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« Reply #7 on: July 08, 2010, 11:52:32 AM »

Agreed.  The G5RV jr. really shines on 40m, 20m, and 17m.  Between the three bands I'd say 20m is the best one.  17m is also fairly good and I've made many contacts with JA stations on 17m.  Many JA stations I worked are running 17m mono-band yagis  Shocked.  40m is decent enough for DX contesting and it served me well over the winter when 20m was dead.  For a compromised antenna I can't complaint!

73,
Jonathan W6GX
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N2QGV
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Posts: 14




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« Reply #8 on: July 09, 2010, 04:53:46 PM »

As it has been said before, you will not know until you try it out.
My TS-2000 internal tuner works on my 102 foot True-Talk G5RV from 75 to 10 with the exception of 30 meters. Just won't do that. My LDG100Pro does 75 to 10, including 30.
If it does not work at first, move the antenna around, higher/lower, or lengthen/shorten your coax into the house. One of those MFJ antenna analyzers would be a big help.
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KF4CZV
Member

Posts: 142




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« Reply #9 on: July 09, 2010, 05:04:11 PM »

Thanks everyone for all the good info! I reckon I'll just try it out and see what happens.

Terry
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